1. Field of the Invention
The present invention relates generally to a training unit for the pacemaker emergency intervention system. Further still, the invention relates to a training unit that provides instructions, coaching, and feedback to a health care provider regarding the pacemaker emergency intervention system.
2. Background of the Invention
In the normal human heart, illustrated in FIG. 1, the sinus (or sinoatrial (SA)) node generally located near the junction of the superior vena cava and the right atrium constitutes the primary natural pacemaker by which rhythmic electrical excitation is developed. The cardiac impulse arising from the sinus node is transmitted to the two atrial chambers (or atria) at the right and left sides of the heart. In response to excitation from the SA node, the atria contract, pumping blood from those chambers into the respective ventricular chambers (or ventricles). The impulse is transmitted to the ventricles through the atrioventricular (AV) node, and via a conduction system comprising the bundle of His, or common bundle, the right and left bundle branches, and the Purkinje fibers. The transmitted impulse causes the ventricles to contract, the right ventricle pumping unoxygenated blood through the pulmonary artery to the lungs, and the left ventricle pumping oxygenated (arterial) blood through the aorta and the lesser arteries to the body. The right atrium receives the unoxygenated (venous) blood from the body. The oxygenated blood from the lungs is carried via the pulmonary veins to the left atrium.
This action is repeated in a rhythmic cardiac cycle in which the atrial and ventricular chambers alternately contract and pump, then relax and fill. Four one-way valves, between the atrial and ventricular chambers in the right and left sides of the heart (the tricuspid valve and the mitral valve, respectively), and at the exits of the right and left ventricles (the pulmonic and aortic valves, respectively, not shown) prevent backflow of the blood as it moves through the heart and the circulatory system.
The sinus node is spontaneously rhythmic, and the cardiac rhythm it generates is termed normal sinus rhythm ("NSR") or simply sinus rhythm. This capacity to produce spontaneous cardiac impulses is called rhythmicity, or automaticity. Some other cardiac tissues possess rhythmicity and hence constitute secondary natural pacemakers, but the sinus node is the primary natural pacemaker because it spontaneously generates electrical pulses at a faster rate. The secondary pacemakers tend to be inhibited by the more rapid rate at which impulses are generated by the sinus node.
Disruption of the natural pacemaking and propagation system as a result of aging or disease is commonly treated by artificial cardiac pacing, by which rhythmic electrical discharges are applied to the heart at a desired rate from an artificial pacemaker. An artificial pacemaker (or "pacer" as it is commonly labeled) is a medical device which delivers electrical pulses to an electrode that is implanted adjacent to or in the patient's heart in order to stimulate the heart so that it will contract and beat at a desired rate. If the body's natural pacemaker performs correctly, blood is oxygenated in the lungs and efficiently pumped by the heart to the body's oxygen-demanding tissues. However, when the body's natural pacemaker malfunctions, an implantable pacemaker often is required to properly stimulate the heart. An in-depth explanation of certain cardiac physiology and pacemaker theory of operation is provided in U.S. Pat. No. 4,830,006.
Pacers today are typically designed to operate using one of three different response methodologies, namely, "asynchronous" (fixed rate), "inhibited" (stimulus generated in the absence of a specified cardiac activity), or "triggered" (stimulus delivered in response to a specified hemodynamic parameter). Broadly speaking, the inhibited and triggered pacemakers may be grouped as "demand" type pacemakers, in which a pacing pulse is only generated when demanded by the heart. To determine what pacing rate is required of the pacemaker, demand pacemakers may sense various conditions such as heart rate, physical exertion, temperature, and the like. Moreover, pacemaker implementations range from the simple fixed rate, single chamber device that provides pacing with no sensing function, to highly complex models that provide fully automatic dual chamber pacing and sensing functions. The latter type of pacemaker is the latest in a progression toward physiologic pacing, that is, the mode of artificial pacing that most closely simulates natural pacing.
Because of the large number of options available for pacer operation, an industry convention has been established whereby specific pacer configurations (or "modes") are usually identified according to a code comprising three or four letters. A fifth coded position may sometimes be used to describe a pacemaker's ability to respond to abnormally high heart rates (referred to as tachycardia). Because most pacemakers do not provide any antitachycardia functions, the fifth coded position is not used in most commonly used pacemaker types. Thus, most common configuration codes comprise either three or four letters, as shown in Table I below. For this reason and for simplicity's sake, the fifth code position is omitted from the following table. Each code can be interpreted as follows:
TABLE I ______________________________________ PACEMAKER CODE DESCRIPTIONS Code position 1 2 3 4 ______________________________________ Function chamber chamber response to programmability, rate Identified paced sensed sensing modulation Options O--none O--none O--none O--none Available A--atrium A--atrium T-- P--programmable V-- V-- triggered M-- ventricle ventricle I--inhibited multiprogrammable D--dual D--dual D--dual C--communicating (A + V) (A + V) (T + I) R--rate modulating ______________________________________
As illustrated in Table I, pacemakers can be programmed or designed to operate in any one of numerous modes of operation. For example, a DDD pacer paces either chamber (atrium or ventricle) and senses in either chamber. Thus, a pacer in DDD mode, may pace the ventricle in response to electrical activity sensed in the atrium. A VVI pacer paces and senses in the ventricle, but its pacing is inhibited by spontaneous electrical activation of the ventricle (i.e., the ventricle paces itself naturally). In VVIR mode, ventricular pacing is similarly inhibited upon determining that the ventricle is naturally contracting. With the VVIR mode, the pacer's pacing rate, however, in the absence of naturally occurring pacing, is modulated by the physical activity level of the patient. Pacers commonly include accelerometers to provide an indication of the patient's level of physical activity. Further still, valid pacemaker modes also include DOO, VOO, AOO, to name but a few.
A complication may arise when a patient with an implanted pacemaker is admitted into a medical facility such as an emergency room. If the patient is experiencing a cardiac-related problem, the examining physician may need to ascertain the mode of operation of the pacemaker in order to diagnose and treat the underlying problem. The patient may not know the mode of operation of his or her pacemaker, and there may not be time for the medical staff to contact the surgeon that implanted the pacemaker or the patient's cardiologist to determine the operational mode programmed for that pacemaker. Even if the initial operational mode of the pacemaker could be ascertained from prior health care professionals, many pacemakers are capable of automatically changing from one mode to another depending on the patient's cardiac needs. Thus, even the surgeon that implanted the pacemaker may have no way of knowing the current operational mode of the patient's pacemaker.
In some instances, however, it is possible to determine the current operational mode of the pacemaker by examining the patient's surface electrocardiogram ("ECG"). A surface ECG, in which adhesive electrodes are placed at various locations on the patient's skin for monitoring the electrical activity of the heart, is commonly performed in medical facilities and, in particular, emergency rooms to determine the physiologoical status of the patient's heart. When a pacemaker emits a pacing pulse to stimulate the heart to beat, that pacing pulse typically manifests itself as a spike on the surface ECG waveform. Thus, it is ocassionally possible to determine the operational mode of the pacemaker by monitoring the pacing spikes on the surface ECG waveform. Some modes of pacemaker operation, however, are so complex that it is nearly impossible to determine the mode of the pacemaker by examining the patient's surface ECG. Even when such a determination is possible, it usually requires a highly specialized physician that may not be available when emergency treatment is needed. Nevertheless, in order to diagnose and properly treat a patient, the need remains for determining the operational mode of an unknown implanted pacemaker quickly and accurately during emergency treatment.
Many pacemakers today have the capability of transmitting information between the implanted pacemaker and an external monitoring device. The communication link typically is bi-directional, permitting data and control signals to be transmitted from the external device to the implanted pacemaker and data to be transmitted by the pacemaker to the external device. Thus, theoretically, a physician or medical technician could determine the operational mode of the pacemaker by using a suitable external monitoring device to request operational mode information from the implanted pacemaker. Although, this approach is theoretically sound, to date it has not been practical because the communication link between an implanted pacemaker and an associated external monitor is customized by each manufacturer. This means that an external monitor manufactured by one pacemaker supplier could not be used to communicate with a pacemaker provided by a different supplier. Consequently, this approach would require the medical facility to have available monitors provided by every pacemaker manufacturer, an absorbatently costly solution. Even if the medical facility had the resources to purchase and maintain external monitors from each pacemaker manufacturer, the examining physician would not know which external monitor to use because he would not know which manufacturer made the pacemaker implanted in the patient.
To remedy this problem, an industry standard has been proposed by the International Organization for Standarization. The standard, entitled ISO/WD 14994, Implants for Surgery-Cardiac Pacemakers-Pacemaker Emergency Intervention System (hereinafter referred to as "PEIS"), requires that all pacemakers manufactured in compliance with this standard include a simple, standard operating mode that can be initiated with a common method. This method is explained in detail in the ISO/WD 14994 standard which is incorporated herein by reference (hereinafter the "PEIS standard"). The PEIS is intended for use in hospital and clinic emergency rooms to permit conversion of conforming implanted cardiac pacemakers to a standard mode (e.g., VVI, VOO) when the pacemaker is perceived by the examining physician to be operating in a non-standard way or in a way not understood by the physician. The PEIS standard refers to the standard operational mode of the pacemaker as the "emergency inhibited mode." Although, the PEIS does not inform the physician of the current pacemaker mode, it does permit the physician to transition any pacemaker (that conforms to the standard) from any mode of operation to a known, simple mode. Once the pacemaker is operating in the known standard PEIS mode, the patient's underlying medical condition can more easily be diagnosed.
As shown in FIGS. 2 and 3, a PEIS assembly 20 defined by the PEIS standard includes a base 22 and a handle 24 attached to the base 22. Base 22 and handle 24 both are constructed of nonmagnetic material, such as plastic. The base 22 includes a bottom surface 26. An annular magnet 30 (FIG. 3) is embedded in the bottom surface 26 of base 22 in accordance with the PEIS standard.
The annular PEIS magnetic 30 has the capability to actuate circuits within a conforming pacemaker, thereby changing the pacemaker's functions to a simple standard mode of operation. The PEIS assembly 20 preferably is mounted on a wall in the vicinity of patients that may need the PEIS. When the examining physician determines that the patient's pacemaker should be placed in the PEIS standard mode of operation, the physician or other medical technician removes the PEIS assembly 20 from the wall and places it on the patient's chest on the site over the implanted pacemaker. This action initiates the "entry code" of the PEIS standard. The implanted pacemaker includes a magnetic field sensor which detects the presence or absence of annular PEIS magnet 30. The PEIS entry code signals the implanted pacemaker to change its mode of operation to the PEIS standard mode. The physician completes the entry code by holding the PEIS assembly 20 in place and then removing it, and repeating this process as illustrated in FIG. 4. The entry code 21 of FIG. 4 takes approximately 13 seconds to complete and includes five steps, each step lasting a predetermined period of time. In the first step 21a, the magnetic is placed on the pacemaker site for 3.+-.1 seconds. The magnetic field sensor in the implanted pacemaker detects the presence of the PEIS magnet 30 and a microprocessor, or other device internal to the pacemaker, measures the period of time in which the magnet is held in place. In step 21b, the magnet 30 is removed from the patient's chest by the physician by a distance of at least 30 centimeters for 2.+-.1 second. The implanted device also measures this period of time. Steps 21a and 21b are repeated in steps 21c and 21d. Finally, the PEIS magnet 30 is placed on the patient for 3.+-.1 seconds in step 21e and then removed. At this point, the physician has provided the entry code to the implanted pacemaker. The pacemaker determines when the magnet is in place and removed, measures the associated time intervals, and if each time interval corresponds to the PEIS standard entry code illustrated in FIG. 4, the pacemaker transitions its current mode of operation to the standard mode required by the PEIS standard. If, however, the correct timing for the entry code has not been provided by the examining physician, the pacemaker will not enter into PEIS standard mode and will remain in its current mode of operation.
According to the PEIS standard, the emergency inhibited mode generally is a VVI mode with a base heart rate of 60.+-.1 pulses per minute ("ppm"). This means that the pacemaker should pace a ventricular chamber at a rate of 60 ppm, but inhibit pacing if the ventrical is able to beat on its own at the target 60 ppm rate. The pacemaker's PEIS emergency inhibited mode also requires the pacemaker to produce a secondary pacing pulse separated from the primary pacing pulse by 80.+-.10 milliseconds ("ms"). This secondary output pulse will have no effect on the cardiac tissue because the secondary pulse will occur at such a time after the primary pulse that the cardiac tissue will not be able to be restimulated by a new pulse. The 80.+-.10 ms spacing is also sufficient to preclude the pacemaker from emitting a secondary pulse in the "vulnerable" period of the cardiac cycle in which a pacemaker pulse could initiate a harmful, and possible lethal, arrhythmia.
Both the primary and secondary pacemaker pulses are visible on the surface ECG. The purpose of the secondary pulse is to provide a visual feedback, via the surface ECG, to the examining physician that the pacemaker has responded to the entry code and is currently in the emergency inhibited mode of operation specified by the PEIS standard. Once the entry code is complete, the pacemaker should then be in a simple mode of operation that is verifiable by the examining physician by monitoring the surface ECG waveform.
When a pacemaker is operating in one of its preprogrammed modes (excluding the PEIS emergency inhibited mode), the PEIS magnet can be used to place the pacemaker in a so-called "magnet mode" of operation. The pacing rate of a pacemaker in the magnet mode is defined by the pacemaker manufacturer. To transition a pacemaker to the magnet mode, the PEIS is placed on the patient's skin over the site of the implanted pacemaker. The pacemaker remains in its magnet mode as long as the PEIS magnet remains on the patient. The pacemaker will revert back to its original mode, however, when the PEIS magnet is removed.
The PEIS standard also requires conforming pacemakers to permit the PEIS magnet to transition the pacemaker from the emergency inhibited mode to an "emergency asychronous mode" in which the pacemaker generates a double pacing pulse (two pulses separated by 80.+-.10 ms) at a base rate of 60.+-.1 ppm. This emergency asychronous mode is initiated after the pacemaker has been placed into the PEIS mode by placing and holding the PEIS magnet in place on the patient's chest over the site of the implanted pacemaker. The pacemaker remains in the emergency asychronous mode as long as the PEIS magnet is held in place on the patient. Pacing is not inhibited while in this mode. When the magnet is removed, the pacemaker will transition back to the emergency inhibited mode.
The PEIS standard requires the magnetic 30 to be a permanent, fixed magnet, and not an electromagnet, which requires electrical power to create the magnetic field. The annular magnet is simple, inexpensive, reliable, and durable. The drawback in requiring a fixed magnet, rather than an electromagnet through which the entry code of FIG. 4 could be automatically generated, is that a human is responsible for ensuring the PEIS magnetic 30 is placed on the patient's chest and removed with the proper timing defined for the PEIS entry code. Although the timing of the entry code is relatively simple, it still requires training to properly and accurately administer the code. Periodic retraining is also necessary. Further still, the examining physician that must initiate the entry code in an emergency situation may not have used the PEIS assembly 20 for an extended period of time, and may need some training in using the PEIS magnetic before attempting to place the patient's pacemaker in the PEIS emergency inhibited mode. Accordingly, the training must be simple and fast.
Thus, a training unit for a PEIS is needed. The training unit should be simple to use and readily available to medical personnel when a patient's pacemaker must be transitioned into the PEIS emergency inhibited mode. Preferably, the training unit should coach the medical professional or technician to perform the entry code and also permit the medical technician to practice the entry code without coaching. Despite the advantages such a training unit would provide, to date no such training unit is known to exist.